Collaborative Research: Unsteady Ground Effect: How Solid Boundaries Affect Bio-Inspired Propulsion

许多动物在水面或海底附近飞行或游泳。这些边界创造了不稳定的、三维的和不对称的流动，可以提高动物的飞行/游泳速度和效率。尽管这些好处有着广泛的影响，但对于接近边界的生物移动，还没有可靠的模型。精确的模型可能会重塑生物学家思考鸟类在开阔水域迁徙的飞行策略或对海底鱼类形状的进化压力的方式。更好地了解近边界的生活方式可以帮助生态学家更好地预测近地生态系统对过度捕捞、栖息地丧失或气候变化的脆弱性。更好的模型还将重塑工程师设计在边界附近运行的仿生汽车的方式。改进这些模型的关键是更好地理解支配近边界游泳和飞行的复杂流动。这项拟议的工作旨在阐明这些复杂的流动，并利用多媒体和一个针对中学女孩的外联计划将它们带入公众的视野。本项目的目标是了解控制近边界游动的非恒定流机制。该项目将通过水道实验和无粘流模拟相结合，支持对非定常地面效应的第一次系统研究。因此，经典的稳定地面效应理论将被推广到游泳和飞行动物中存在的现代跨学科流动现象。这些流动现象将通过测试斯特劳哈尔数、减少的频率、纵横比、波动和不对称运动学对近地面游泳的影响来探索。这项研究将集中于四个具体目标：(I)发展近地游泳力和能量学的标度定律，(Ii)绘制近地三维流动相互作用图，(Iii)确定波动运动学在近地游泳中的作用，以及(Iv)了解不对称运动学如何改变近地流动。通过包括实验和无粘性模拟，这项研究将确定哪些影响是雷诺数相关的，哪些是纯粹由无粘性涡旋动力学驱动的。这项研究将提供对鱼类近地生活方式的关键见解，并将有助于设计新型的生物启发水下机器人。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Many animals fly or swim near the surface of water or the ocean floor. These boundaries create unsteady, three-dimensional, and asymmetrical flows that can increase the animal's flying/swimming speed and efficiency. Despite the wide implications of these benefits, there are no reliable models for near-boundary bio-locomotion. Accurate models could reshape the way biologists think about the flight strategies of birds migrating over open water or the evolutionary pressures on the shapes of bottom-dwelling fish. A better understanding of near-boundary lifestyles could help ecologists better predict the fragility of near-ground ecosystems to over-fishing, loss of habitat, or changing climate. Better models would also reshape the way engineers design bio-inspired vehicles that operate near boundaries. The key to improving these models is a better understanding of the complex flows governing near-boundary swimming and flying. The proposed work aims to shed light on these complex flows and bring them into public view using multimedia and an outreach program for middle school girls. The goal of this project is to understand the unsteady flow mechanisms governing near-boundary swimming. The project will support the first systematic study of unsteady ground effect through a combination of water channel experiments and inviscid flow simulations. As a result, classic steady ground effect theory will be generalized to the modern interdisciplinary flow phenomena present in swimming and flying animals. These flow phenomena will be explored by testing the effects of Strouhal number, reduced frequency, aspect ratio, undulation, and asymmetric kinematics on near-ground swimming. The research will focus on four specific aims: (i) developing scaling laws for the forces and energetics of near-ground swimming, (ii) mapping near-ground three-dimensional flow interactions, (iii) determining the role of undulatory kinematics in near-ground swimming, and (iv) understanding how asymmetrical kinematics alter near-ground flows. By including both experiments and inviscid simulations, the research will identify which effects are Reynolds-number dependent and which are driven purely by inviscid vortex dynamics. This research will provide key insights into the near-ground lifestyles of fish and will aid in the design of novel bio-inspired underwater vehicles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.